Soil foundations - Geotechnical Investigation and Design Tables - page 276

•

Assumptions on frictional angles:
- Loose - 30 ◦ .
- Medium Dense - 33 ◦ .
- Dense - 37 ◦ .
- Very Dense - 40 ◦ .

21.17 Pile shaft resistance in coarse material based on
N - value

•

Estimates of the pile shaft resistance in granular materials can be determined from
the corrected SPT N - value.

•

The N - value is the average corrected value along the length of the pile.

Table 21.17 Pile shaft resistance in granular materials (Meyerhof, 1976)

Type of pile Displacement Shaft resistance (kPa)

Driven High to average eg concrete and including sheet piles 2 N

Driven Low eg Steel H piles N

Bored Negligible 0.67 N

21.18 Pile base resistance in coarse material based on
N - value

•

Estimates of the pile base resistance in granular materials can be determined from
the corrected SPT N - value.

•

The N - value is the corrected value for 10D below and 4 D above the pile point.

•

D = Diameter of pile.

•

L = Length of pile in the granular layer.

Table 21.18 Pile base resistance in granular materials (Meyerhof, 1976).

Type of pile Type of soil Base resistance (kPa)

Driven Fine to medium sand 40 N L/D 400 N

≤

Driven Coarse sand and gravel 40 N L/D

≤

300 N

Bored Any granular soil 14 N L/D

21.19 Pile interactions
•

The driving of piles in sands increases the density around the piles depending on
the soil displaced (depending on the diameter of pile). Adjacent and later piles are
then more difficult to install. Steel H piles are considered low displacement.

•

The driving of piles in clays may produce heave.

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The spacing can be reduced if pre-drilling is used.